dashboard: set cookie_secure in grafana

When using grafana behind https `cookie_secure` should be set to `true`.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1966880

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 4daed1f)

roles/ceph-grafana/templates/grafana.ini.j2

@@ -27,3 +27,8 @@ http_addr = {{ grafana_server_addr }}
 admin_user = {{ grafana_admin_user }}
 admin_password = {{ grafana_admin_password }}
 allow_embedding = {{ grafana_allow_embedding }}
+
+{% if dashboard_protocol == 'https' %}
+[session]
+cookie_secure = true
+{% endif %}